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b=grBMCrKszZ6CLCD/+93t0prKH7inVqyLu36vLX/4gz9rcYuUFzRKw5/L33Y0yDdINR3XPc kSf9K4JRxZbi3FCA== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id D906D136D9; Tue, 22 Sep 2026 05:41:58 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id /hu1JSYVsmrGbAAAD6G6ig (envelope-from ); Tue, 22 Sep 2026 05:41:58 +0000 Message-ID: <94d29ac5-d01a-49c3-8001-96798452ca80@suse.de> Date: Tue, 22 Sep 2026 07:41:58 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 6/8] block: don't fall back to buffered I/O for atomic writes To: Tal Zussman , Jens Axboe , Christoph Hellwig , Johannes Thumshirn , Luis Chamberlain , Hannes Reinecke , "Matthew Wilcox (Oracle)" , John Garry , Christian Brauner , "Darrick J. Wong" , Keith Busch , "Martin K. Petersen" Cc: Shin'ichiro Kawasaki , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko References: <20260921-blkdev-fixes-v4-0-e2801f71ede9@columbia.edu> <20260921-blkdev-fixes-v4-6-e2801f71ede9@columbia.edu> Content-Language: en-US From: Hannes Reinecke In-Reply-To: <20260921-blkdev-fixes-v4-6-e2801f71ede9@columbia.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Score: -4.51 X-Rspamd-Queue-Id: 625A01F390 X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Level: X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; RCPT_COUNT_TWELVE(0.00)[16]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[columbia.edu:email,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.de:dkim,suse.de:email,suse.de:mid,sashiko.dev:url]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Flag: NO On 9/22/26 4:54 AM, Tal Zussman wrote: > blkdev_direct_write() turns an -EBUSY from page cache invalidation into > a 0 return, so an IOCB_ATOMIC write is retried in full through > blkdev_buffered_write(), with no atomicity guarantee. > > Skip the buffered fallback in blkdev_write_iter() for IOCB_ATOMIC, as > it already does for IOCB_NOWAIT, so the -EBUSY case returns -EAGAIN and > the caller retries, matching __iomap_dio_rw(). > > ext4 has the same fallback and only warns in it. For block devices the > fallback can be skipped before any I/O is submitted, so fail early > instead. > > Fixes: caf336f81b3a ("block: Add fops atomic write support") > Reported-by: Sashiko > Link: https://sashiko.dev/#/patchset/20260802-blkdev-fixes-v1-0-a82fc549fd74%40columbia.edu?part=2 > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Tal Zussman > --- > block/fops.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/block/fops.c b/block/fops.c > index 90777e8a9a6c..7f23778f6b81 100644 > --- a/block/fops.c > +++ b/block/fops.c > @@ -766,10 +766,11 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from) > if (iocb->ki_flags & IOCB_DIRECT) { > ret = blkdev_direct_write(iocb, from); > if (ret >= 0 && iov_iter_count(from)) { > - if (iocb->ki_flags & IOCB_NOWAIT) { > + if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_ATOMIC)) { > /* > * The buffered fallback blocks on i_rwsem and > - * on writeback of the data it copied: return > + * on writeback of the data it copied, and > + * can't provide torn-write protection: return > * the short direct write instead and let the > * caller retry. > */ > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich